This report describes studies on the biochemical, biophysical, and physiological mechanisms of membrane transport in the kidney, the regulation of these transport systems by hormones and various pathophysiological effectors, and the changes which occur in renal function in aging. The findings relate to investigations on: 1. Sodium-proton exchange activity in the aging rat. 2. Thyroid hormone regulation of sodium-proton exchange activity. 3. Renal adaption in metabolic acidosis. 4. Adrenergic regulation of metabolism. 5. Identification and characterization of ion channels in non-excitable tissues.